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Ch.2 - Atoms & Elements
Chapter 2, Problem 98

The ratio of the mass of a nitrogen atom to the mass of an atom of 12C is 7:6, and the ratio of the mass of nitrogen to oxygen in N2O is 7:4. Find the mass of 1 mol of oxygen atoms.

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First, we need to understand that the mass of an atom of 12C (carbon-12) is exactly 12 atomic mass units (amu) by definition. Given that the ratio of the mass of a nitrogen atom to the mass of an atom of 12C is 7:6, we can set up a proportion to find the mass of a nitrogen atom. Let's denote the mass of a nitrogen atom as 'N'. So, we have N/12 = 7/6.
Next, solve the proportion for 'N' to find the mass of a nitrogen atom in atomic mass units (amu).
Then, we know that the ratio of the mass of nitrogen to oxygen in N2O is 7:4. This means that for every 7 parts of nitrogen, there are 4 parts of oxygen. Since there are two nitrogen atoms in N2O, the mass of one nitrogen atom is half of the total nitrogen mass in N2O. So, we can set up another proportion: (N/2) / O = 7/4, where 'O' is the mass of an oxygen atom.
Solve this proportion for 'O' to find the mass of an oxygen atom in atomic mass units (amu).
Finally, to find the mass of 1 mol of oxygen atoms, multiply the mass of an oxygen atom (in amu) by Avogadro's number (6.022 x 10^23). This is because 1 mole of any substance contains Avogadro's number of particles (atoms, in this case).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Atomic Mass and Molar Mass

Atomic mass is the mass of an individual atom, typically measured in atomic mass units (amu). Molar mass, on the other hand, is the mass of one mole of a substance, expressed in grams per mole (g/mol). Understanding these concepts is crucial for converting between the mass of atoms and the mass of moles, which is essential for solving stoichiometric problems.
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Mass Ratios in Compounds

Mass ratios in compounds indicate the relative masses of different elements within a compound. In the question, the mass ratio of nitrogen to oxygen in N2O is given as 7:4, which allows us to set up a relationship between the masses of nitrogen and oxygen. This concept is fundamental for determining the mass of one mole of oxygen based on the provided ratios.
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Stoichiometry

Stoichiometry is the area of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It involves using ratios derived from balanced chemical equations to calculate the amounts of substances involved. In this question, stoichiometry is applied to find the mass of oxygen based on the mass ratios provided for nitrogen and oxygen.
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